COS 5-9
Biodiversity and colonization dynamics of macrofauna in a deep-sea methane seep metacommunity
The metacommunity framework is increasingly used to examine mechanisms influencing community assembly and the maintenance of biodiversity. This framework is suited to the consideration of both local species and environmental interactions and spatial processes such as dispersal that link otherwise disconnected patches. Deep-sea chemosynthetic ecosystems such as methane seeps are patchy, spatially hierarchical, and characterized by extreme physicochemical gradients, providing an opportunity to utilize metacommunity theory to examine the structure and maintenance of biodiversity. Hydrate Ridge (west of Oregon) contains methane seeps at depths of 580–800 meters. We focused on invertebrate macrofauna on hard substrates, primarily carbonate rocks that are microbially-precipitated in seep ecosystems. We used submersibles to deploy bare substrates, and one year later collected them to compare the colonization assemblage with that on natural carbonates from Hydrate Ridge. A combination of site-by-species incidence matrices, variance partitioning, and ranked-abundance plots of colonizing macrofauna were used to analyze metacommunity patterns for both colonization and natural substrates. Specifically, we ask 1) whether metacommunity patterns at methane seeps suggest consistent community structure and diversity patterns across spatial scales and environmental conditions; and 2) do particular idealized mechanistic models appear especially relevant to certain microhabitats or taxonomic groups within chemosynthetic ecosystems?
Results/Conclusions
From an observational standpoint, site-by-species incidence matrices suggest that colonization substrates (early successional processes) introduce novel patterns to the overall metacommunity on natural seep carbonates, as they are clearly separated by ordination processes. Decomposing total community variation into environmental and spatial components indicates that beta diversity is well explained by seep chemical activity and substrate type, but not spatial filters. Finally, ranked abundance plots reveal striking differences in the suites of species colonizing areas of active seepage versus inactive areas without seepage. Substrates at active sites are likely to be colonized by seep endemic species, especially dominant gastropod species that graze on large bacteria, while colonization at inactive sites is not dominated by any particular taxonomic group and may be slightly more “random” with respect to species abundance. These results lead us to conclude that environmental filtering is important for explaining colonization dynamics and biodiversity at localized methane seep patches, but surrounding inactive areas. No one statistical tool allows community patterns to reveal dynamical structuring processes, but using multiple analytical tests increases our ability to interpret likely diversity-maintaining processes at methane seeps.